New US antitrust chief William Baer yesterday sued to block A-B from buying Grupo Modelo — the maker of Corona beer — saying the merged company would have too much pricing power.

“Beer prices have gone up in recent years because of [the] high concentration of brewers,” the Department of Justice antitrust boss said.

Modelo, according to Justice, has not lifted prices of its Corona beer in the past several years, which has kept Anheuser-Busch and MillerCoors prices in check.

A-B and MillerCoors control about 65 percent of the US beer market and adding Modelo — whose Corona is the No. 1 import in the country — would boost that share to 72 percent, the DoJ alleges.

Anheuser-Busch is not taking the lawsuit lying down.

“We remain confident in our position, and we intend to vigorously contest the DoJ’s action in federal court,” the company said.

Baer’s aggressive move comes within his first month on the job. In fact, his first two decisions at the DoJ were to block mega-mergers. The other involved the Bazaarvoice-PowerReviews deal.

With the Anheuser-Busch deal, the former antitrust head at Arnold & Porter, a law firm known for its corporate work, is not only taking on a politically influential company, but also throwing down a direct challenge to a recent DoJ antitrust boss — Christine Varney.

Varney was antitrust chief from 2009 through August 2011 and is now one of the lead counsels for Modelo law firm Cravath, Swaine & Moore and is pushing to get the deal approved.

In addition, Sharis Pozen, who followed Varney in the job until last July, is now at Skadden Arps, which represents Anheuser-Busch.

“This is Varney’s first prominent case since leaving the DoJ,” one antitrust lawyer not involved in the case said.

This is not the first time Baer — known up to now as General Electric’s lawyer of choice on antitrust matters — has moved to block a deal between two giant consumer brands.

While at the Federal Trade Commission from 1995 to 1999, Baer successfully sued to block Staples’ acquisition of Office Depot.

If this suit goes to trial, one antitrust lawyer said it wouldn’t be a slam-dunk for Baer. “A-B will argue that the market is highly competitive and entry is not difficult,” he said.

Regulators will focus on how A-B and MillerCoors have hiked prices, including in summer 2011 when A-B delayed a planned price increase in New York because Modelo dropped the price of Corona.

A-B alone has the choice of whether to challenge the deal in court since Modelo cannot legally walk away from the deal until the end of the year, a source said.

A-B will owe Modelo a $725 million break-up fee if the deal falls through, the same source said.